1. Field of the Invention
The present invention relates to a heat spreader module for cooling an IC chip or the like which comprises semiconductors, etc.
2. Description of the Related Art
Generally, a heat spreader module for effectively dissipating the heat of a semiconductor device such as an IGBT (Insulated Gate Bipolar Transistor) or the like comprises a circuit board, an insulating board, a heat spreader member (heat diffusion layer), and a pedestal. If necessary, stress dampening layers may be disposed between these components of the heat spreader module. Heretofore, it has been customary to join these components with a solder layer (having a melting point of about 250° C.).
However, the solder layers pose a large heat resistance, and the manufacturing cost for the heat spreader module is high because of two joining processes required, i.e., a process of brazing the circuit board and the insulating board to each other and a process of joining the joined assembly to the pedestal.
The inventor of the present invention has disclosed, in Japanese laid-open patent publication No. 2002-43482, a process of joining a circuit board, an insulating board, an intermediate layer, and a heat sink with an active hard brazing material under pressure and heat all in one sequence, leaving no joining layers which would pose a heat resistance. According to the disclosed process, a heat spreader module having a high thermal conductivity can be manufactured inexpensively.
According to the above process of completing the joining of the components in one sequence, if the active hard brazing material is excessively supplied, then excess active hard brazing material is squeezed out around the pedestal when the components are joined. The need to remove the squeezed active hard brazing material results in an increase in the manufacturing cost.
The melted hard brazing material that is squeezed out is brought into contact with side edges of copper plates that are used as the circuit board and the dampening layers. When the active hard brazing material and the copper plates contact each other, they are alloyed, and the alloyed region has an electric conductivity and a thermal conductivity lower than those of copper, or has durability increased to make the stress dampening capability lower than that of copper, resulting in a reduction in the quality of the heat spreader module.
One solution is to reduce the supplied amount of the active hard brazing material for preventing excess active hard brazing material from being squeezed out around the pedestal. However, a reduction in the supplied amount of the active hard brazing material tends to cause a shortage of the absolute amount of active elements required to join the components, giving rise to a new problem in that a necessary bonding strength cannot be achieved.